More than pollutant removal: constructed wetlands and waste stabilization ponds as biodiversity hotspots and community assets in Tanzania

Abstract

Waste stabilization ponds (WSPs) and constructed wetlands (CWs) are important ecotechnologies for wastewater treatment. Despite their potential and wastewater management being challenging in urban and peri-urban areas of Tanzania, their adoption and sustainability is not well developed. This study examined (a) social knowledge, attitude, and perceptions (KAPs) on wastewater treatment, technologies involved, and reuse across municipal wastewater treatment plants in four regions of Tanzania; (b) biodiversity of birds, insects, and reptiles in constructed wetlands (CWs) and waste stabilization ponds (WSPs), and (c) bacterial abundance and diversity in different types of CWs. A semi-structured household-level questionnaire (n=327) was used to collect quantitative and qualitative data. The survey involved observations and face-to-face interviews to assess social KAPs on wastewater treatment, technologies, reuse, and potential health risks. Key informants were selected purposively (n=8). The study also employed point counts, direct observations, and camera traps to assess bird diversity in WSPs and CWs. Direct observation and pitfall traps along established transects were used to collect and assess insects and reptiles. Fishnet was used to assess the reptiles living in the WSPs. Additionally, wastewater was collected in four different CWs for bacterial diversity establishment. Community KAPs were analyzed using SPSS, while Jamovi and PAST software were used to analyze the diversity and abundances of birds, insects, and reptiles, whereas bacterial community composition was characterized using Illumina-based sequencing of the V3 and V4 hypervariable region of 16S rRNA. The results show that social KAPs surrounding wastewater treatment and reuse were sufficient based on the KAPs score achieved from the asked questions. However, the general knowledge of treatment technologies, processes and reuse risks was found to be low. Over 90% of respondents were unaware of wastewater treatment technologies and the potential health risks associated with using treated wastewater (59%). Multivariate analysis of variance revealed significant differences (P < 0.05) in KAPs for treated wastewater across different demographic variables examined, i.e., age, sex and education level. Furthermore, results showed that birds exhibit high species abundance (n = 1132), high species richness, Margalef index (D = 4.266), evenness (E = 0.815), Shannon diversity (H = 2.881) and Simpson index (λ =0.903). The abundance and diversity of studied groups differed significantly (P<0.05) between WSPs and CWs. In addition, the results showed that the Proteobacteria were dominant (48.66%) phyla across all CWs. The Gammaproteobacteria class (27.67%), the family Comamonadaceae (35.79), and the genus Flavobacterium (4.35%) were dominant in all examined CWs.